The present invention relates to a device for driving rollers in automatic machines.
In particular, the invention relates to a device for driving the rollers of an automatic machine employed in the manufacture of filter cigarettes, referred to generally as a filter tip attachment, to which reference is made explicitly throughout the following specification albeit implying no limitation in scope. In effect, the invention would find application to equal advantage, for example, in a drive system used to producing the continuous rotation of wrapping turrets in packer machines.
Conventionally, when manufacturing filter tipped cigarettes in a machine of the type in question, each one of a first succession of sticks, cut from a cigarette rod and spaced apart a predetermined distance one from the next, is joined at a rolling station by way of a connecting element of sheet material to one of a second succession of sticks cut likewise from a cigarette rod, thus fashioning an intermediate tobacco product describable as a xe2x80x9cdouble cigarettexe2x80x9d. Each such double cigarette appears as two sticks of cigarette rod separated one from the other by a double filter plug; the plug is united to the two sticks by the connecting element, which consists in a band of paper material cut transversely from a continuous strip decoiled from a roll, a central part of the band enveloping the double filter plug and the two endmost parts wrapped each around one end of a respective stick. The double cigarettes assembled in this way are directed in succession through a cutting station where each double cigarette is severed transversely into two halves, thereby generating two columns of oppositely oriented single cigarettes disposed with the respective filters adjacent and substantially in contact one with another. The two columns of cigarettes advance thereupon into an overturning station where the cigarettes of one column are flipped onto the cigarettes of the other column to obtain a single column of cigarettes, identically oriented, which are advanced through an outfeed of the filter tip attachment and toward the infeed of a packer.
In general, conventional filter tip attachments of the type mentioned above include a train of feed rollers rotatable about mutually parallel axes and constituting the aforementioned rolling stations. Each such roller affords a plurality of suction flutes distributed uniformly about the periphery, each of which designed to take up and advance one relative tobacco product in a direction transverse to its longitudinal axis.
Each roller of the type outlined above comprises a shaft set in rotation by a gear coupled to one end, also a first internal tubular body disposed coaxial with the shaft and connected rigidly by one end to a bulkhead of the machine frame. The roller also comprises at least one second external tubular body associated with the first tubular body by way of respective rolling bearings; the second tubular body is disposed thus coaxially with the internal body, and connected rigidly to the aforementioned shaft by which it is driven in rotation about an axis common to both tubular bodies.
The single roller is equipped also with a vacuum duct to which the suction flutes distributed about the periphery of the external second tubular body can be connected by way of a longitudinal cavity formed internally of the first tubular body and a plurality of relative holes afforded by the second tubular body, thereby enabling each flute to retain a respective tobacco product through the force of suction for a given duration, even in the presence of actions that tend during operation of the filter tip attachment to dislodge the stick from the flute currently occupied, whether due to gravity, or to the considerable centrifugal force generated by the high angular velocity of the single rollers.
In a typical arrangement the rollers are mounted overhung, each supported by a respective shaft of which the bearing block is positioned in a housing afforded by a vertical bulkhead of the machine.
The torque required to set the roller in rotation is transmitted to the shaft generally by a gear, associated rigidly with one end of the shaft on the side of the bulkhead remote from the roller.
In addition to the product feed rollers described above, a filter tip attachment comprises other types of rollers driven in rotation, for example a set of rollers serving to feed and apply the band of tipping paper by which the filter is wrapped and joined to the stick of cigarette rod. These rollers likewise are carried by respective shafts and set in rotation by corresponding gears associated with the ends of the shafts on the side of the vertical bulkhead opposite from the rollers.
It will be evident from the foregoing description that, in addition to supporting the rollers, the vertical bulkhead described above also functions as a partition, separating the rollers on the one side from the respective gears, which are enclosed in one or more-housings on-the other side and arranged substantially in a continuous train timed in such a way as to guarantee the necessary synchronization of the various rollers.
Given that the high output capacity of filter tip attachments-used in modern machines is associated with the higher and higher rotational speeds of the components used in their construction, lubrication is an aspect of great importance and a key factor in determining correct operation of the machine overall. Accordingly, such machines incorporate a complex network of pipelines, installed normally at the rear, carrying fluid by which the gears are lubricated individually. The gears require forced lubrication moreover, and accordingly the machine must be equipped internally with hydraulic pumps connected to the network of pipelines, also with respective vessels in which the lubricant is held and recirculated.
One of the main drawbacks-connected with this type of lubrication derives from the fact that in order to lubricate the numerous moving parts, a complex system of seals is needed for each roller; these seals must also be inspected periodically and renewed when necessary in order to maintain their efficiency, inasmuch as any-wear or accidental damage resulting in-an impairment of integrity could cause the lubricant to leak onto the rollers and penetrate the flutes accommodating the sticks. The tobacco product would inevitably then be soiled by the lubricant and a relatively large quantity would have to be rejected for each operating cycle of the machine completed.
To the end of overcoming this drawback, designers of filter tip attachments, and indeed of machines in many other art fields, have sought to replace the train of gears driving the rollers by coupling each roller to a respective electric motor, thereby eliminating the gear. Whilst the problems connected with lubrication are overcome by this expedient, another problem is introduced, namely the bulk of the electric motors, since the shaft of each motor must be coupled to the shaft of~the roller and the motor itself mounted by cantilevering the frame from the vertical bulkhead.
Other drawbacks are linked to the utilization of individual electric motors coupled to the shafts of the single rollers: the considerable difficulties experienced in controlling the motors in such a manner as to ensure faultless synchronization of the rollers making up the train so that the tobacco products proceed smoothly from one station to the next and the various manufacturing operations are performed correctly on each one; also the high cost of the motors themselves, which are required in number equal to the number of rollers installed in the machine (not inconsiderable) and.thus tend to impact decisively on the overall cost of the machine.
The object of the invention is to provide a drive system for the rollers of automatic machines that is of comparatively compact dimensions, free from the lubrication-related problems mentioned above, simple in embodiment and economical.
The stated object is duly realized in a device according to the present invention for driving the rollers of automatic machines, wherein each roller comprises at least one first tubular body rigidly associated with the machine, also a second tubular body placed coaxially over the first tubular body and rotatable relative to the selfsame first tubular body about a common axis of rotation.
Advantageously, the device disclosed comprises electric drive means incorporated into each single roller, consisting in at least one inductor member associated rigidly with one first or second tubular body, and at least one inducible member associated rigidly with the remaining first or second tubular body.